The present invention relates to gas turbine engine fuel nozzles and, more particularly, to pilot fuel injectors of engine fuel nozzles.
Aircraft gas turbine engines include a combustor in which fuel is burned to input heat to the engine cycle. Typical combustors incorporate one or more fuel injectors whose function is to introduce liquid fuel into an air flow stream so that it can atomize and burn.
Staged combustors have been developed to operate with low pollution, high efficiency, low cost, high engine output, and good engine operability. In a staged combustor, the nozzles of the combustor are operable to selectively inject fuel through two or more discrete stages, each stage being defined by individual fuel flowpaths within the fuel nozzle. For example, the fuel nozzle may include one or more pilot stages, and a main stage that only operates at higher engine power levels. The fuel flowrate may also be variable within each of the stages.
The main stage includes an annular main injection ring having a plurality of fuel injection ports which discharge fuel through a surrounding centerbody into a swirling mixer airstream.
Known types of pilot fuel injector structures include pressure atomizer fuel injectors and air blast fuel injectors.
Prior art designs have used two-stage pilots with both stages being pressure atomizers. This configuration allows for good lightoff/starting performance owing to its small flow number pilot primary tip and good flow range owing to its larger pilot secondary. However, the close coupling of these circuits means that for all intents and purposes they are only a single fuel stream when both are flowing and provide no capability for flame temperature control. Furthermore, the pilot secondary flow actually disrupts the pilot primary atomization resulting in poor sub-idle efficiency.
Other prior art designs have used a prefilming air blast (PAB) pilot which provides better atomization performance than a pilot secondary pressure atomizer.
Accordingly, there remains a need for a pilot fuel injector with both good lightoff capability and a secondary that does not interfere with primary atomization as it is brought into operation.